The overall goal of this proposed project is to define how the CREB transcription factor relays hormonal and environmental signals in the mammalian testis to genes within Sertoli and germ cells during spermatogenesis. The specific hypothesis to be tested is that alterations in the relative concentrations of activator and repressor CREB isoforms in the seminiferous tubules regulate the expression of cAMP-inducible genes required for the expansion and differentiation of male germ cells. One objective is to define the mechanisms responsible for the stage-specific expression of various CREB isoforms during the maturation of germ cells. A second objective of this study is to identify "target" genes expressed in Sertoli and germ cells that are regulated by the cAMP signaling pathway and the CREB transcription factor.